1. Field of the Invention
The present invention relates to polyglycerol alkyl ether nonionic surfactants that exhibit superior emulsifying activities on a variety of oils and solvents; and to nonionic surfactant compositions containing the polyglycerol alkyl ether nonionic surfactants.
2. Description of the Related Art
Aromatic nonionic surfactants prepared via addition polymerization of ethylene oxide (EO) to alkylphenols exhibit very superior emulsifying activities and have thereby been used in a wide variety of fields. However, adverse affects of aromatic nonionic surfactants on the environment and ecosystems have been noticed. The aromatic nonionic surfactants have thereby been more and more replaced with aliphatic nonionic surfactants prepared from aliphatic alcohols as raw materials, in the fields typically of detergents where due consideration must be given to the environment and ecosystems.
As aliphatic nonionic surfactants prepared from aliphatic alcohols, there are known alkylene oxide adducts that are prepared by carrying out addition polymerization of ethylene oxide and an alkylene oxide having three or four carbon atoms to an aliphatic alcohol in the presence of a base catalyst or acid catalyst. The alkylene oxide adducts have already been used typically as detergents, emulsifiers, emulsifiers for emulsion polymerization, dispersants, solubilizers, wetting/swelling agents, and antifoaming agents (see Japanese Unexamined Patent Application Publication (JP-A) No. Hei 7-126690).
However, these nonionic surfactants having polyoxyethylenes or polyoxypropylenes as hydrophilic groups, if used in general consumable articles such as cosmetics and detergents, give emulsions that are not so stable with time and liable to undergo phase separation. This is because the association force between water and a polyoxyethylene chain or a polyoxypropylene chain is weak, whereby the hydrophilicity significantly varies depending on temperature.
To solve the problem of temporal stability of emulsions, a variety of emulsification processes has been investigated. An exemplary process is a process in which the oil/water interfacial tension is minimized by passing through regions where an infinite association of molecules is formed, such as a liquid crystalline phase, a surfactant phase (D phase), and a phase transition temperature (a phase reversal temperature) region, to thereby form fine, homogeneous emulsification particles. These processes are, however, all complicated and thereby suffer from low production efficiency. Specifically, there has been found no aliphatic nonionic surfactant which is an aliphatic nonionic surfactant being environmentally friendly, which has a superior surface activity equivalent to those of aromatic nonionic surfactants, and which can exhibit, via an easy and simple operation, such a superior emulsifying activity stably over time.